1. Field of the Invention
The present invention relates to an inductance structure intended to be used, for example, in low-noise amplifiers, mixers, voltage-controlled oscillators, passive filters, transformers, etc.
2. Discussion of the Related Art
To obtain an inductance having a significant value but which takes up a small surface area, a possibility is to form the inductance loops with metal tracks, belonging to different metallization levels, which are more or less stacked along a privileged direction.
An inductance generally comprises two main access terminals. For certain applications, in addition to the main access terminals, it is desirable to have an additional access terminal at the level of a specific point of the inductance for which the voltage between the additional access terminal and one of the main access terminals is opposite to the voltage between the additional access terminal and the other main access terminal. Such a point is called the inductance midpoint and the additional access terminal is called the differential access terminal. The midpoint actually corresponds to the inductance point for which the inductive and resistive components of the inductance between one of the main access terminals and the midpoint are identical respectively to the inductive and resistive components of the inductance between the midpoint and the other main access terminal.
It is desirable for the inductance to have a structure enabling simply and systematically determining the position of the midpoint. As an example, when the inductance is formed of a single circular loop, with the two opposite ends of the loop forming the main access terminals, the midpoint corresponds to the loop point diametrically opposite to the main access terminals. However, as soon as the inductance comprises loops formed by metal tracks of several metallization levels, it may be difficult to simply and systematically determine the midpoint position. A difficulty is due to the fact that the materials used to form the metal tracks may be different from one metallization level to the other. As an example, for certain CMOS processes, aluminum may be used for the last metallization level while copper may be used for the other metallization levels. Another difficulty results from the fact that the thicknesses of the metal tracks may be different from one metallization level to the other.
Further, it is desirable for the midpoint to be easily accessible, that is, generally for the midpoint to be on a loop located at the periphery of the inductance.